1. Field of the Invention
This invention relates in general to rolling shutters and has specific reference to a rolling shutter for roof window, of the type comprising an apron movable in a substantially horizontal plane and made of blades having their lateral ends slidably engaged in guide rails constituting the prolongation of a casing rigidly fixed to the sash-frame of the rolling shutter, this casing enclosing a first shaft for rolling-up and/or unrolling the apron and another shaft constituting the drive shaft disposed downstream of said first shaft and provided at either ends with a cam wheel having an angular backlash consistent with the variable pitch existing between the dogs of two adjacent blades of said apron.
2. The Prior Art
It is already known through the document EP-A-O No. 145,628 to provide a roof window rolling shutter comprising an apron movable in a substantially horizontal plane and made of a plurality of blades having their lateral ends slidably engaged in lateral guide rails in prolongation of a casing rigid with the sash-frame of the rolling shutter and enclosing a first shaft for rolling-up and/or unrolling the apron and a second shaft disposed downstream of said first shaft, said second shaft being provided at either end with a cam wheel having an angular backlash consistent with the variable pitch existing between the dogs of two adjacent blades of said apron.
In this known structure the casing bottom is connected to the guide rails by means of a ramp on which the apron blades are adapted to slide upwards toward the rolling-up and/or unrolling shaft, the contact generatrix being disposed in the lower portion of this shaft.
However, this rolling shutter cannot be used for equipping roof windows comprising a sash of the type pivoting about a horizontal hinge axis. In fact, the apron cannot be rolled up unless the central longitudinal axis of the winding shaft is raised with respect to the guide rails. Now this requirement implies a considerable increment in the overall height of the casing. On the other hand, for obvious lighting reasons, roof windows have a frame projecting more or less above the roofing surface, a feature constituting an interference to the free flow of rainwater and/or snow. Thus, this obstacle is aggravated by the presence of a relatively high casing, and the inconvenience of a defective flow of rainwater and/or snow is increased considerably.
Besides, when a foreign body such as a stone or the like is deposited on the apron, it is carried towards the winding shaft and liable to be wedged between two adjacent turns of the apron. Thus, the diameter of the rolled-up portion of the apron is increased unduly and the casing is too small to accomodate this increment. Under these conditions, the apron is damaged or jammed, and cannot be driven freely.